The present invention relates generally to non-volatile memory devices and in particular the present invention relates to a synchronous non-volatile flash memory.
Memory devices are typically provided as internal storage areas in the computer. The term memory identifies data storage that comes in the form of integrated circuit chips. There are several different types of memory. One type is RAM (random-access memory). This is typically used as main memory in a computer environment. RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only to read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost.
Computers almost always contain a small amount of read-only memory (ROM) that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to. An EEPROM (electrically erasable programmable read-only memory) is a special type non-volatile ROM that can be erased by exposing it to an electrical charge. Like other types of ROM, EEPROM is traditionally not as fast as RAM. EEPROM comprise a large number of memory cells having electrically isolated gates (floating gates). Data is stored in the memory cells in the form of charge on the floating gates. Charge is transported to or removed from the floating gates by programming and erase operations, respectively.
Yet another type of non-volatile memory is a Flash memory. A Flash memory is a type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. Many modern PCS have their BIOS stored on a flash memory chip so that it can easily be updated if necessary. Such a BIOS is sometimes called a flash BIOS. Flash memory is also popular in modems because it enables the modem manufacturer to support new protocols as they become standardized.
A typical Flash memory comprises a memory array that includes a large number of memory cells arranged in row and column fashion. Each of the memory cells includes a floating gate field-effect transistor capable of holding a charge. The cells are usually grouped into blocks. Each of the cells within a block can be electrically programmed in a random basis by charging the floating gate. The charge can be removed from the floating gate by a block erase operation. The data in a cell is determined by the presence or absence of the charge in the floating gate,
A synchronous DRAM (SDRAM) is a type of DRAM that can run at much higher clock speeds than conventional DRAM memory. SDRAM synchronizes itself with a CPU""s bus and is capable of running at 100 MHZ, about three times faster than conventional FPM Fast Page Mode) RAM, and about twice as fast EDO (Extended Data Output) DRAM and BEDO (Burst Extended Data Output) DRAM. SDRAM""s can be accessed quickly, but are volatile. Many computer systems are designed to operate using SDRAM, but would benefit from non-volatile memory.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a non-volatile memory device that can operate in a manner similar to SDRAM operation.
The above-mentioned problems with memory devices and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
In one embodiment, the present invention provides a non-volatile synchronous flash memory that is compatible with existing SDRAM package pin assignments. It will be apparent from reading the detailed description that system designers with knowledge in SDRAM applications could easily implement the present invention to improve system operation. In one embodiment, a synchronous memory device comprises an array of memory cells arranged in rows and columns, a clock connection to receive an externally provided clock signal, and control circuitry to perform a first read operation of a first row of the array in response to a first externally provided active command, and perform a second read operation on a second row of the array in response to a second externally provided active command. The control circuitry does not require a precharge time period during a time period between the first and second externally provided active commands.
In another embodiment, a synchronous memory device comprises an array of memory cells arranged in rows and columns, a clock connection to receive an externally provided clock signal, and control circuitry to perform a first read operation on a first row of the array to output data from the first row on an external connection during a clock signal transition. The control circuitry is adapted to receive a read active command on the clock signal transition to initiate a read operation of a second row of the array.
A method of operating a synchronous flash memory device is also provided. The method comprises receiving a first active read command and a memory array first row address on a first clock signal transition, initiating a first memory read operation in response to the first active read command, and receiving a read command and a memory array column address on a second clock transition that is a first predetermined number of clock transitions following the first clock signal transition. The method further comprises providing data on a data connection that was read from the memory array at the first row address. The data is provided on a third clock transition that is a second predetermined number of clock transitions following the second clock signal transition. A second active read command and a memory array second row address are received on the third clock signal transition, and a second memory read is initiated in response to the second active read command.